The overall objective of this project is to improve our understanding of the nature of the body protein losses, which frequently accompany severe injury or surgery, in order to minimize these losses. The emphasis will be on the losses experienced by older people. In order to obtain this objective we are studying differences in requirements for certain nutrients (esp. protein and amino acids) between young adult and old laboratory animals, the incorporation of amino acids into protein in cultures of primary cells obtained from young, mature and old animals, and the effect of specific nutrients (so far, certain trace minerals and amino acids) on losses of body protein following severe trauma. Easy access to the feed is of extreme importance in order to maintain feed intake of old animals and permit valid comparisons. Urinary urea appeared not to be a useful indicator of nitrogen sufficiency of older animals, necessitating use of a nitrogen balance technique. Supplementation of a 4.5 percent mixture of non-essential amino acids and ammonium citrate was not only not equivalent to a 6 percent protein diet for mature rats, but did, at least in one case, promote less nitrogen retention than an unsupplemented 4.5 percent protein diet. Skin fibroblasts for the tissue culture study were successfully obtained by the explant method and kidney and heart cells by serial trypsinization. Traumatized rats given an arginine plus glycine supplement showed highly significant increases in urinary creatine excretion in comparison to the creatine excretion prior to trauma or of non-traumatized rats, while creatinine excretion remained relatively constant. BIBLIOGRAPHIC REFERENCES: Thompson, H.J., P. Griminger, and J.L. Evans. Effect of dietary copper, manganese, and zinc on nitrogen equilibrium and mineral distribution subsequent to trauma in mature rats. J. Nutr., vol. 106: 1421-1428, 1976. Sitren, H.S., and H. Fisher. Nitrogen retention in rats fed on diets enriched with arginine and glycine. I. Improved nitrogen retention after trauma 2. Effect of diethyl ether anesthesia on nitrogen retention. Brit. J. Nutition, vol. 37, March 1977.